Extension of Pulsewidth Modulation From Carrier-Based to Dither-Based

The carrier-based pulsewidth modulation (PWM) is extended to a dither-based PWM by replacing a conventional triangular carrier with a binary dither signal. Such a simple extension is generally impractical due to serious performance degradation. However, this paper presents a novel binary dither generator that helps enhance the performance of the dither-based PWM and makes the idea possible. The binary dither is generated as determined by the sign of the filtered modulation noise. The dither generated in this way automatically eliminates low-frequency modulation noise and randomizes the switching frequency. As indicated by experiments, the resulting dither-based PWM has relatively lower THD+N and less pronounced high-frequency switching harmonics, as compared with the conventional fixed-frequency triangular carrier PWM.

I. Introduction

Pulse width modulation (PWM) is a method for carrying information on a train of pulses by varying pulsewidth. To the best of the authors' knowledge, it was first described in 1931 by American engineers H. Shore and his colleagues as a means of transmitting intelligence [1]. Not very long thereafter, the PWM method was developed for radio and telephone communication [2], [3], and later, with the introduction of sampled-data control, the method also found an application in control systems as a way to sample regulation errors and generate relay control forces [4], [5]. In the late 1960s, some pioneering research on PWM motor drive led to the realization of the vast potential and utility of PWM in power amplification and conversion [6]–[8], and since then, PWM has been an invaluable technique in the field of power electronics.